Estimation of the Heat Flow Variation in the Chad Basin Nigeria

Wireline logs from 14 oil wells from the Nigerian sector of the Chad Basin were analyzed and interpreted to estimate the heat flow trend in the basin. Geothermal gradients were computed from corrected bottomhole temperatures while the bulk effective thermal conductivity for the different stratigraphic units encountered in the wells were computed from the sonic logs data. The heat flow values were then calculated. A corrected average geothermal gradient of 3.4 oC/100 m and a regional range of 3.0 to 4.4 oC/100 m were obtained. A porosity range of2 to 79 % and average of 35 % were computed for Chad Basin Nigeria. Also the thermal conductivities vary from 1.70 and 3.11 Wm-1 oC-1, with an average value of 2.35 Wm-1 oC-1 computed for the various wells in the basin. A large variation in heat flow was recorded within the basin. Mean heat flow values computed for the basin vary from 63.6 to105.6 mWm-2, with a simple average of 80.6 mWm-2. Although there is no distinct trend on heat flow within the basin, the computed heat flow values are relatively lower at the southwestern and northeastern axis of the basin. And the values obtained in this study compared favorably with those of other world sedimentary basins (including NigerDelta) that are of similar history with the Chad Basin, suggesting that the Nigerian Chad Basin is a possible petroliferous basin

Inkjet printed multimetal microelectrodes on PDMS for functionalized microfluidic systems

A novel direct method of metal microelectrode patterning on polydimethylsiloxane (PDMS) using inkjet printed gold and silver nanoparticles to form electrochemical sensors is presented. Inkjet printing is an additive microfabrication technique enabling microelectrode patterning directly over large areas at low-temperatures. (3-mercaptopropyl) trimethoxysilane (MPTMS) to promote PDMS surface wettability and improve metal adhesion and a pixel-printing subsampling method to overcome surface tension driven ink-droplet coalescence, are then employed to form a robust fabrication process. The resulting printed gold and silver microelectrodes exhibit good compactness, continuity and conductivity, and are used to manufacture functionalized microfluidic systems with in-situ three-electrode electrochemical sensors.published_or_final_versio

An interstitial fluid transdermal extraction system for continuous glucose monitoring

A novel microfluidic system which is fabricated with five polydimethylsiloxane layers for interstitial fluid (ISF) extraction, collection, and measurement toward the application of continuous and real-time glucose monitoring is presented in this paper. The system consists of a micro vacuum generator for ISF transdermal extraction and fluid manipulation, micro chambers for the collection of ISF, micro pneumatic valves for fluid management, and a micro flow sensor for ISF volume measurement. Sequentially controlled by the pneumatic valves, the ISF extraction, collection, and volumetric measurement functions of the system were demonstrated using the stable vacuum generated by the integrated vacuum generator. Through low-frequency ultrasound pretreated full-thickness pig skin, the normal saline solution with different glucose concentrations was transdermally extracted, collected, and measured. The absolute error in the volume measurement of the transdermally extracted ISF analog was less than 0.05 μ L. The microfluidic system makes it possible to realize the clinical application of continuous glucose monitoring based on ISF transdermal extraction technology. © 2012 IEEE.published_or_final_versio

An explicit hybridizable discontinuous Galerkin method for the 3D time-domain Maxwell equations

International audienceWe present an explicit hybridizable discontinuous Galerkin (HDG) method for numerically solving the system of three-dimensional (3D) time-domain Maxwell equations. The method is fully explicit similarly to classical so-called DGTD (Dis-continuous Galerkin Time-Domain) methods, is also high-order accurate in both space and time and can be seen as a generalization of the classical DGTD scheme based on upwind fluxes. We provide numerical results aiming at assessing its numerical convergence properties by considering a model problem and we present preliminary results of the superconvergence property on the H curl norm

Gill Na+, K+-ATPase as a function of size and salinity in the blue crab, Callinectes sapidus Rathbun

Some kinetic properties of gill Na+,K+-ATPase of the blue crab, Callinectes sapidus, and its relation to osmotic regulation in juvenile and adult crabs were analyzed. Results suggest the presence of some differences in transport mechanisms for juvenile and adult blue crabs to maintain hemolymph concentration in dilute media. Adult and sub-adult crabs demonstrated fairly low levels of Na+,K+-ATPase activity in both anterior and posterior gills regardless of acclimation salinity. Juvenile blue crabs had much higher levels of Na+,K+-ATPase activity in both anterior and posterior gills relative to adults. Crabs acclimated to low salinity showed a significant increase in enzyme activity, both in anterior and posterior gills. The levels of enzyme activity in the anterior gills of juveniles showed a marked increase at low salinities. Enzyme activity in the posterior gills of juvenile crabs at 150 mOsm increased (35%) over sea water. However, there is a markedly higher specific activity increase (80%) in the anterior gills of smaller, juvenile crabs at this lower salinity. Sex had no effect on the enzyme activity relative to salinity. Abrupt transfer of juvenile and adult crabs from 1000mOsm to 150mOsm resulted in a gradual change in the Na+,K+-ATPase activity that reached steady-state levels within 7-10 days after the transfer. The time course for the increase in activity was preceded by an increase in the expression of the Na+,K+-ATPase a-subunit mRNA. The Na+,K+-ATPase of the posterior gills of both juvenile and sub-adult crabs showed an increased affinity for ATP at lower salinities, while that of the posterior gills of juvenile crabs had a higher affinity for Na+ than that of sub-adults at low salinity

Probing the switching mechanism in ZnO nanoparticle memristors

We investigate the resistance switching mechanism in memristors based on colloidal ZnO nanoparticles using electroabsorption (EA) spectroscopy. In this EA experiment, we incorporate a small amount of low-bandgap polymer, poly(9,9-dioctylfluorene-cobenzothiadiazole) (F8BT), as a probe molecule in ZnO-nanoparticle memristors. By characterizing this polymer, we can study the change of built-in potential (VBI) in the device during the resistance switching process without disturbing the resistance state by the EA probe light. Our results show that VBI increases when the device is switched to the high resistance state, suggesting a shift of effective workfunction of the electrode. Thus, we attribute the resistance switching to the field-dependent migration of oxygen vacancies associated with the adsorption and desorption of oxygen molecules at the Al/ZnO interface. This process results in the modulation of the interfacial injection barrier which governs the resistance state of the device.This work was supported by the Engineering and Physical Sciences Research Council [Grant Number EP/G060738/1]Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article "Probing the switching mechanism in ZnO nanoparticle memristors" has been accepted by Journal of Applied Physics. After it is published, it will be found at http://scitation.aip.org/content/aip/journal/ja

OPTICAL CHARACTERIZATION OF INHOMOGENEITIES IN BLUE-EMITTING INGAN/GAN MQWS

The growth of blue-emitting InGaN/GaN MQWs, the system setup of a low temperature PL/EL/IV system for temperature dependent PL/EL/IV spectroscopy, and the system setup of a CLSM with nanometer-scale spectrum measurement and TRPL measurement abilities are described. A range of temperature-dependent PL experimental work, CLSM imaging experimental work and TRPL experimental work on blue-emitting InGaN/GaN MQWs are presented. In temperature-dependent PL measurements, the decreasing of spectrum- integrated PL intensity with increasing temperature is explained with a two-nonradiative- channel model, in which the two nonradiative channels correspond to the thermal activation of carriers out of the strongly localized states and the weakly localized states, respectively. The ‘S-shaped’ red-blue-red shift of PL peak energy and the ‘inverse S- shaped’ change of PL FWHM when temperature increases from 10 K to 300 K are explained with carrier localization and carrier dynamics. CLSM imaging and nanometer-scale PL spectral measurements show that the PL intensity fluctuates in micrometer scale, and that the bandgap energy in bright region is tens of meV smaller than that in dark region. The small-bandgap-energy regions are localization centers which limit the diffusion of the carriers and prevent carriers from diffusing to the NRRCs. Nanometer-scale TRPL measurements are conducted on blue-emitting InGaN/GaN MQWs for the first time, as far as the author knows. The measurements show that both bright region and dark region are characterized by two lifetimes: fast decay lifetime t1 is smaller than 3 ns and slow decay lifetime t2 is longer than 10 ns. The fast decay with shorter lifetime t1 corresponds to the carrier localization in weakly localized states, where the radiative recombination is more quenched by NRRCs and also competes with carrier transfer intro strongly localized states. And the slow decay with longer lifetime t2 corresponds carrier localization in strongly localized states. The fact that both fast decay and slow decay exist in both bright region and dark region indicates that both bright region and dark region has small bandgap energy fluctuation in themselves. Measurements show that the slow decay lifetime t2 in bright region is longer than that in dark region, indicating a higher probability of nonradiative recombination in dark region or carrier transporting from dark region to bright region. Measurements show that larger bandgap energy difference between small- bandgap-energy regions and large-bandgap-energy regions provides stronger carrier localization effect, via the presence of higher CLSM image average intensity, larger PL intensity ratio and longer smaller-bandgap-energy slow decay lifetime t2 when larger bandgap energy difference occurs. The effect of MOCVD growth parameters on MQW bandgap energy fluctuations and average intensity was analyzed. It was found out that by increasing growth pressure, decreasing growth rate, increasing growth temperature, increasing effective V/III ratio, and increasing gas speed, the bandgap energy difference between bright region and dark region increases, leading to higher average PL intensity

Directed forgetting in a proactive interference paradigm

"One explanation of the benefit of directed forgetting is the reduction of proactive interference (PI) from the first list during encoding of the next list. To explore this possibility, I used a forget instruction in a release from PI paradigm. The forget instruction did not reduce the PI on subsequent lists as measured by the immediate tests usually given in this paradigm in Experiments 1-3. The other variable manipulated in this study was the recall tests. A reverse test effect was found on a final recall measure in Experiment 2. Immediate recall tests in a PI paradigm may already serve as an implicit forget cue to the participants. This finding has implications for both directed forgetting and proactive interference research."--Abstract from author supplied metadata

Reasoning about recognizability in security protocols

Although verifying a message has long been recognized as an important concept, which has been used explicitly or implicitly in security protocol analysis, there is no consensus on its exact meaning. Such a lack of formal treatment of the concept makes it extremely difficult to evaluate the vulnerability of security protocols. This dissertation offers a precise answer to the question: What is meant by saying that a message can be "verified''? The core technical innovation is a third notion of knowledge in security protocols -- recognizability. It can be considered as intermediate between deduction and static equivalence, two classical knowledge notions in security protocols. We believe that the notion of recognizability sheds important lights on the study of security protocols. More specifically, this thesis makes four contributions. First, we develop a knowledge model to capture an agent's cognitive ability to understand messages. Thanks to a clear distinction between de re/dicto interpretations of a message, the knowledge model unifies both computational and symbolic views of cryptography gracefully. Second, we propose a new notion of knowledge in security protocols -- recognizability -- to fully capture one's ability or inability to cope with potentially ambiguous messages. A terminating procedure is given to decide recognizability under the standard Dolev-Yao model. Third, we establish a faithful view of the attacker based on recognizability. This yields new insights into protocol compilations and protocol implementations. Specifically, we identify two types of attacks that can be thawed through adjusting the protocol implementation; and show that an ideal implementation that corresponds to the intended protocol semantics does not always exist. Overall, the obtained attacker's view provides a path to more secure protocol designs and implementations. Fourth, we use recognizability to provide a new perspective on type-flaw attacks. Unlike most previous approaches that have focused on heuristic schemes to detect or prevent type-flaw attacks, our approach exposes the enabling factors of such attacks. Similarly, we apply the notion of recognizability to analyze off-line guessing attacks. Without enumerating rules to determine whether a guess can be "verified'', we derive a new definition based on recognizability to fully capture the attacker's guessing capabilities. This definition offers a general framework to reason about guessing attacks in a symbolic setting, independent of specific intruder models. We show how the framework can be used to analyze both passive and active guessing attacks

Medium access control for inter-gateway handoff support in multi-hop wireless mesh networks

Wireless mesh networks (WMNs) have emerged to be a key wireless technology to support large-scale wireless Internet access. Seamless inter-gateway handoff support is an essential issue to ensure continuous communications in multi-hop WMNs. When the movement of a mobile mesh node (MN) causes its attachment point change in the Internet, the complete handoff process may include two steps: the link-layer handoff and the network-layer handoff. During the network-layer handoff, network- layer signaling packets need to be transmitted between the MN and the Internet via the multi-hop wireless mesh backbone. Due to the multi-hop transmission of network- layer handoff signaling packets, the handoff performance in WMNs can be largely degraded by the long queueing delay and medium access delay at each mesh router, especially when the backbone traffic volume is high. However, this critical issue is ignored in existing handoff solutions of multi-hop WMNs. In addition, the channel contention between data packets and handoff signaling packets is not considered in existing medium access control (MAC) designs. In this research, the seamless handoff support is addressed from a different perspec- tive. By eliminating channel contentions between data and handoff signaling pack- ets, the queueing delay and channel access delay of signaling packets are reduced, while data throughput is maintained. Since various WMNs have different channel resources and hardware cost requirements, four MAC schemes are proposed to im- prove the multi-hop handoff performance in single-channel single-radio, single-channel multi-radio, multi-channel single-radio, and multi-channel multi-radio WMNs. With the proposed MAC schemes, the inter-gateway handoff performance can be improved significantly in multi-hop WMNs